F. H. Lahee — Metamorphism and Geological Structure. 363 



The degrees of metamorphism may now be studied with 

 reference (1) to rock texture ; (2) to geographical distribution ; 

 (3) to stratigraphic depth ; and, (4) to deformation. Follow- 

 ing this, the relations of the schistosity to the bedding, a 

 subject closely allied to (4), just mentioned, will receive con- 

 sideration. 



-Relations of the Degree of Metamorphism to Rock 



Texture. 



A comparison of the degrees of metamorphism in rocks of 

 coarse and fine grain from different parts of the Basin would 

 be unprofitable, for many other factors might enter to disguise 

 the true relations. Such a comparison must obviously be one 

 of purely local significance. 



Theoretically, shales, being finer than sandstones, should 

 yield to folding first ; and, since folding implies more or less 

 rearrangement of the rock particles (deformation by flowage 

 or by minute fracture), metamorphism should also commence 

 first in the shales. This statement would seem to indicate 

 that, in a series of strata which differ from one another in 

 texture, the finer beds would be more intensely crumpled,* 

 and hence more highly metamorphosed, than the coarser beds, 

 after a given period of time, metamorphism being in process 

 all the while. 



What are the conditions in the Narragansett Basin ? From 

 each of twenty-two localities visited in the field work, two or 

 more specimens of different texture were obtained. Follow- 

 ing is a list of these specimens : 



General 



locality 



Just north 



Conglomerates. 



Stage of 

 metamorphism 



Sandstones. 



Stage of 



metamorphism 



Shales. 



Stage of 



metamorphism 



of C : 1 



B 



B 



c 



E : 1 



A 



A 



— 



H : 4 



— 



A 



A 



G :5 



B 



B 



— 



C : V 



— 



D 



C 



B: 9 



C 



C 



c 



E : 9 



— 



D 



c 



B : 11 



— 



C 



c 



C : 12 



— 



C 



D 



D : 10 



— 



D 



D 



D : 11 



— 



D 



C 



E : 11 



— 



C andD 



C 



E : 12 



D 



— 



B 



* See remarks on competent structure and reference thereto in Part I of 

 this paper. This Journal, last number, p. 254. 



